Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating recording media to reduce the coercivity of the media so that the applied magnetic writing field can more easily direct the magnetization of the media during the temporary magnetic softening of the media caused by the heat source. A tightly confined, high power laser light spot is used to heat a portion of the recording media to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the media at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
One approach for directing light onto recording media uses a planar solid immersion mirror (PSIM), or lens, fabricated on a planar waveguide; and a near-field transducer (NFT), in the form of an isolated metallic nanostructure, placed near the PSIM focus. The near-field transducer is designed to reach a local surface plasmon (LSP) condition at a designated light wavelength. At LSP, a high field surrounding the near-field transducer appears, due to collective oscillation of electrons in the metal. Part of the field will tunnel into an adjacent media and get absorbed, raising the temperature of the media locally for recording.
A laser diode can be used as the light source for HAMR. If a vertical cavity surface emitting laser (VCSEL) is used as the light source in HAMR, then a grating can be used to couple light from the VCSEL into the planar solid immersion mirror (PSIM) waveguide. The current limitation to using a VCSEL is that they don't supply enough power for current HAMR head design requirements (−50 mW). In order to obtain more laser power from the VCSEL, the output window of the VCSEL must be enlarged. However, there is only a finite amount of space on the end of the slider to contain both the PSIM and the grating. This limits the maximum size of the VCSEL output window.
There is a need for improved coupling of light from a VCSEL into a planar solid immersion mirror (PSIM) waveguide.